Liquid crystal display devices (LCD devices) have such advantages as a possibility of remarkably reduced thickness, low power consumption, and facility for full-colorizing, compared with other display devices such as CRTs (Cathode Ray Tubes).
With these advantages, LCD devices have recently been used for various types of apparatuses such as mobile phones, notebook-sized computers, portable TVs, and digital video cameras.
Among the LCD devices, active matrix LCD devices such as TFT (Thin Film Transistor) -LCD devices have been in the dominant position thanks to their quick responsiveness and high display qualities.
As the demand for active matrix LCD devices increases, the performance requirement for the same has become higher year by year. Above all things, there has been a great deal of interest in reducing the power consumption of active matrix LCD devices.
Actually, the power consumption of active matrix LCD devices is an important factor in designing rapid-growing portable devices like mobile phones and PDAs (Personal Digital Assistants), so that the reduction of the power consumption of active matrix LCD devices is urgently needed.
Methods of the reduction of the power consumption and the improvement of the display qualities have been actively researched. For instance, such methods of reducing the power consumption are explained in publications including Japanese Laid-Open Utility Model Application No. 60-50573/1985 (Jitsukaisho 60-50573; published on Apr. 9, 1985) and Japanese Laid-Open Patent Application No. 10-10489/1998 (Tokukaihei 10-10489; published on Jan. 16, 1998). These publications focus on the method of transmitting a television signal, so that, utilizing a vertical blanking interval during which period no data exists, the reduction of the power consumption is achieved by stopping the operation of peripheral drive circuits during a vertical blanking interval.
This vertical blanking interval is originally provided as a period during which period an electron beam from the electron gun inside a CRT returns to a previous position, so as not to be required in LCD devices at all. However, for receiving a television signal such as NTSC on the occasion of displaying normal televisual images, LCD devices are also provided with the vertical blanking interval.
An alternative method of reducing the power consumption is explained in Japanese Laid-Open Patent Application No. 6-342148/1994 (Tokukaihei 6-342148; published on Dec. 13, 1994), wherein ferroelectric liquid crystal which functions as a memory is utilized for a liquid crystal panel so that the refresh rate is reduced.
However, the conventional methods disclosed by the above-referenced publications have problems as follows.
In the case of the method of stopping the operation of peripheral drive circuits during the vertical blanking interval disclosed by Japanese Laid-Open Utility Model Application No. 60-50573/1985 and Japanese Laid-Open Patent Application No. 10-10489/1998, as the former publication suggests, the vertical blanking interval is only around 8% of the total time and hence merely 5% of the electric power can be saved in the interval.
In the method disclosed by Japanese Laid-Open Patent Application No. 6-342148/1994, the ferroelectric liquid crystal is basically for binary (black and white) display so as not to allow gray scale display, and hence it is not possible to display realistic images. Moreover, since the production of ferroelectric liquid crystal display panels requires highly advanced techniques, practical use thereof has not been realized yet.
As just described, conventional driving methods of active matrix LCD devices hardly achieve the reduction of the power consumption, while keeping basic display qualities such as brightness, contrast, responsiveness, and gray scale property.